A slide sheet e.g.
https://www.completecareshop.co.uk/moving-and-handling/glide-and-slide-sheets/
is useful.
You may be able to get one through whoever organised the bed.
If you use one don't leave it on the floor, they are designed to be very slippy.
Yes, slide sheets are great as well, sometimes I use that, or with the carers, when they are here. The good thing about the Wendylett sheets is that they stay in place all the time, so you don't have to roll to get them under the person, or remove the top one after the manoeuvre. The fitted bottom sheet has a slidey top surface and the top, flat sheet, a slidey bottom surface. If course as soon as you start sitting someone up in bed, they slide down, but you can control that to some degree by tucking the very wide sides in. I thought these were issued as standard to all with a hospital bed. We only had one set originally and I had to ask for a second set. I also bought a third set on ebay. They are ridiculously expensive, around £300 for the two, but we got the two sets from the OTs.
I'm not actually 100% sure about this advice to only have one layer on the airflow mattress. The DNs told me that the mattress would not work as well, ie. not as beneficial for the skin, if there were multiple layers on the mattress. Maybe it's more important for someone who is totally bed bound, but the fact remains that if someone's pad leaks, you have to take measures, either disposable bed pads or washable kylie sheets. I can't see that more layers compromise the effectiveness of the airflow mattress, unless they were to be very thick layers of course.
You do have to be very careful with slide sheets - we nearly had mum slip off the bed on one once!